In the technology for connecting optical fibers, there has been known, in the name of “mechanical splice”, an optical fiber connecting device capable of permanently connecting together the uncoated fiber elements of optical fibers from which the sheaths are removed in a manner that their end surfaces are abut together in concentric without relying upon the melt-adhesion or adhesion. The optical fiber connecting device of this type, usually, is equipped with a fiber-element securing member having opposing holding surfaces that can be opened and closed to firmly hold the uncoated fiber elements of the optical fibers, at least either one of the opposing holding surfaces having a linear guide groove (e.g., a V-groove having a V-shape in cross section) for holding the uncoated fiber element of the optical fiber at a predetermined position. In carrying out the connection operation, the uncoated fiber elements of the pair of optical fibers are inserted in the guide grooves in the opposing holding surfaces of the fiber-element securing member that is opened in a condition where their ends are abut together (or an abutment condition). In this state, a pressure is exerted on the fiber-element securing member from the outer side, whereby the uncoated fiber elements of the two optical fibers are firmly secured in the opposing holding surfaces with the application of a required pressure so as to be permanently connected together in concentric in the guide grooves.
There has been known an optical fiber connecting device of this type comprising a body with cavity, a fiber-element securing member held in the cavity of the body in a manner that it can be opened and closed, and an actuating member mounted in the cavity of the body in a manner that it can be moved to open and close the fiber-element securing member (see, for example, Patent Document 1 (JP Pat. No. 2713309)). In the body are formed a pair of passages which are in concentric and aligned with each other, and being opened in the outer surfaces thereof and communicated with the cavity. The uncoated fiber elements of the pair of optical fibers are introduced in the corresponding passages and are guided into the fiber-element securing member. In conducting the connection operation, the actuating member is completely pushed into the cavity of the body to apply pressure to the fiber-element securing member which is opening at a position where the uncoated fiber elements of the pair of optical fibers are abut together at their ends and to move the fiber-element securing member to the closed position. Accordingly, the fiber-element securing member strongly secures the uncoated fiber elements of the two optical fibers in an abutment condition with the application of a required pressure and, thus, the pair of optical fibers are permanently connected together in a concentric manner.
With the optical fiber connection device disclosed in the Patent Document 1, the optical fibers that are to be connected are uncovered at their ends during the fiber connection operation over the regions longer than the lengths that are to be held by the fiber-element securing member. Therefore, the pair of optical fibers securely connected together through the optical fiber connecting device have their uncoated fiber element portions and the neighboring sheath portions that are received in their corresponding passages without being substantially locked, If the tensile action or twisting action is exerted on the optical fibers, the tensile stress or the twisting stress is concentrated on the uncoated fiber element portions that are arranged in the passages of the body without being locked, and the uncoated fiber elements may be damaged or broken, which may cause an optical loss. In order to avoid the stress from concentrating on the uncoated fiber elements, therefore, an optical fiber connecting device has been proposed comprising a sheath holding mechanism capable of securing the sheath portions of the optical fibers onto the body on the outer side of the fiber-element securing member (see, for example, Patent Document 2 (U.S. Pat. No. 5,638,477)).
In the optical fiber connecting device disclosed in the Patent Document 2, a pair of slots are formed in the body separately from the cavity so as to be communicated with a pair of passages in the body, and clip members having a U-shape in cross section are mounted in the slots in a manner to be displaced. Each clip member has a pair of arms facing each other maintaining a predetermined gap, and the sheath portion of the optical fiber arranged in the passage is received between these arms with the application of pressure. When the optical fibers are to be inserted in the passages of the body, the clip members are placed at positions where their both arms will not interfere with the sheaths of the optical fibers. After the uncoated fiber elements of the pair of optical fibers are held by the fiber-element securing member, the slip members are completely pushed into the corresponding slots in the body, whereby the sheath portions of the optical fibers in the passages are inserted into between the two arms of the clip members while being compressed, and the sheath portions are secured to the body. The sheath holding mechanism in the optical fiber connection device has also been disclosed in the specification of Japanese Patent Application No. 2002-240836 (see also U.S. patent application Ser. No. 10/522,003), which is a prior application filed by the present applicant.